Automatic radio listener survey system



July 339 19:53 w. D. HORN Sir-AL AUTOMATIC RADIO MSTENER SURVEY SYSTEM Filed Marcil la, :,947

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S k S S SS wn lNvENToRS Wm. Z. Harn i ORNEY E951 W, HQRN Es-AL 2225559754 AUTOMATIC RADIO LSTENER SURVEY SYSTEM med Maron la, 1947 4 sheets-snaai 2 INJENTORS' July 3, 1951 w. D. HORN x-:rAL

AUTOMATIC RADIO LISTENER SURVEY SYSTEM Filed March 18, 1947 4 Sheets-Sheet 5 ORNEY July 3, 1951 w. D. HORN Erm.

AUTOMATIC RADIO LISTENER SURVEY SYSTEM 4 Sheets-Sheet 4 Filed March 18, 1947 INVENTORS Wm. Horn. I 9- J/E. Ra @zzz/7l ATTORNEY Patented July 3, 195:1

AUTOMATIC RADIO LISTENER SURVEY SYSTEM William D. Horn and John R. Ragazzini, New York, N. Y.; said Ragazzni assignor to said Horn Application March 18, 1947, Serial No. 735,441

(Cl. 23S- 52) 12 Claims.

This invention reiates to an automatic radio listener survey system and more particularly to a system for making an automatic record at frequent intervals ci the operation of a number of radio receivers which are tuned to a given radio broadcast.

An object of the invention is to provide a system of the above type which automatically records at a central point the tuning of many different radio receivers.

Another object oi the invention is to provide a ystem of the above type which is operated automatically without the aid of special signals from the broadcast stations and consequently does not require the cooperation of the broadcast companies.

Another object is to provide va system of the above type which makes a substantially continuous record of the number of selected radio receiving sets tuned to the diierent radio broadcasts.

A not ier object is to provide a system of the above type having novel and improved details of construction and features of operation.

Various other objects and advantages will be apparent as the nature of this invention is more fully disclosed.

In accordance with the present invention, the control is eiiected in response to a recurring normal characteristic of the broadcast program as distinguished from a special control signal which might be transmitted in addition to the regular program. Such normal characteristic may comprise a selected audio frequency note or series of notes, a selected audio volume level or a selected p wer level of the carrier or intermediate frequency. in a specic embodiment the silent periods are utilized for the control. Such periods may, for example, constitute the intervals between words of a spoken program or the rests in musical program. We have found that such silent intervals sometimes occur simultaneously in a, plurality of programs, such as at the beginning and end of the program period. In order to prevent registration during such simultaneous silent periods, we provide means for rendering the recording apparatus ineffective `when a silent period appears on more than one program at the same time.

More specifically, we provide at selected radio receivers a control circuit which is connected to the audio output of the receiver and is provided With means for producing a control signal for actuating a relay during intervals of Zero audio frequency output. The relay connects a predetermined reactive load to the power line for a predetermined short interval of time which is independent of the length of the period of silence. For example, the reactive load may be connected for a. period of a selected fraction of a second, although the period of silence which instigated the connection of the reactance may have lasted for only -`a small portion of that time or may have continued beyond that period.

These automatically controlled reactors are installed in a, selected number of receivers in localities supplied by a central power station, for example, a thousand receivers which may be distributed throughout the community.

For recording the total number of reactors which are connected across the power line at any one instant, a series of central monitors are provided Which control automatic var meters for measuring the reactivefvolt-amperes of the line. A separate monitor is provided for each broadcasting station or network to be monitored. Each monitor is tuned to the broadcast station which is to be monitored thereby and includes an audio frequency circuit which, like the home receiver, is adapted to produce a control signal during periods of audio frequency silence. This control signal is connected to actuate a var meter which is capable oi measuring and recording the increment in reactive-volt-amperes on the power line during the period oi measurement.

In order to prevent the system from recording during periods when reactors are on the power line simultaneously in response to silences on two or more broadcast stations, each monitor Ialso includes means for producing an inhibiting signal for a Xed period after the onset of a silence. During the fixed period after the onset of =a silence on each monitors respective program the monitor `sends out an inhibiting signal which prevents other monitors from recording. When these fixed periods on dierent monitors overlap, no monitor can record because each monitor inhibits the others.

Hence each monitor makes a continuous record of the reactive load thrown on the power line in response to the p riods of silence on its respective broadcast program, but records only when it receives no inhibiting signals from other monitors.

Although the novel features which are characteristic of this invention are pointed out more particularly in the claims, the nature of the invention will be better understood by referring to the following description, taken in connection with the accompanying drawings in which a specic embodiment of the invention has been set forth for purposes of illustration.

In the drawings:

Fig. 1 is a block diagram illustrating a monitoring system embodying the present invention;

Fig. 2 is a schematic circuit diagram of the home receiver unit; and

Figs. 3 and 4,'taken together, are a schematic circuit diagram of the central monitor system.

Referring rst to Fig. 1, the home receiver ill is shown as connected to an antenna li and supplied with. power from an AC'power line i2. The receiver is provided with an audio frequency output line lll of the usual character. To this line an audio frequency control deviceA l5 is connected through an audio frequency transformer i6. The audio frequency control device is adapted to respond to the audio frequency output of the receiver l@ and to produce a control signal during zero audio frequency output periods. The control signal is supplied through output lines il to actuate a timed relay E8 which is adapted to connect an inductive load i9 across the alternating current power supply line l2 and to maintain the load connection for a predetermined period regardless of the duration of the control signal. It is to be understood that one of the units is connected to each of the selected radio receivers which are to be registered.

At a central point, a plurality of monitors are provided,` two of which are shown in Fig. 1. Each monitor'comprises a receiver fit, connected to an antenna 2i and to an audio frequency control circuit 22 which is adapted, during periods of audio frequency output silence, to supply a control signal Ythrough a line23 to a signal genera torZfl, and to supply an inhibiting signal through a line 25 to the signal generators 2@ oi' the other monitors. The signal generator 2li is adapted, when actuated by the control signal, to produce a timed signal having a definite duration. This timed signal is supplied to a trigger circuit 2@ which in turn is connected to actuate a var meter 2l' which isA connected tothe power supply line l2 and is adapted to measure the reactive-voltamperes thereon. The var meter 2l is connected to are'corder'. The power line l2 may of course be three phase and has been shown as a single phase line for Vconver'iience only.

` A' numberv of these monitors are provided, corresponding to the number of radio networks and unaffiliated stations to be monitored. Each monitor system is adapted to measure theY inductive load on the power line only during a Xed period after the'onset of a silent period on its particular broadcast program. During these periods the inductive loads le of the various home units which are tuned to that station are connected across the line. Consequently, the total added reactive load is a measure of the number of home units which are tuned to that particular broadcast station.

One embodiment of the home unit receiver circuit is shown in more detail in'Fig. 2. Referring to Fig. 2, a standard radio broadcast receiver 3? is shown as connected to an antenna 3l and is supplied with an audio output line connected to the primary 32 of an audio frequency transformer 33 having a secondary 3d connected in series circuit with a resistor 35 and a rectifier tube36'. The resistor 35 is connected through a biasing battery 3l to ground at 38, and by a line et to the control grid il of an amplier tube 42.

The tube 42 is shown as a pentode having. a cathode llt connected to ground at M, a screen grid 45 connected through a resistor 46 and a shunt condenser il to a source of positive biasing potential, a suppressor grid i8 connected to the cathode 53, and an anode i9 which is connected by a line 5; through a coil 5i of a slow acting relay 52 to a source of positive plate potential. rlhe relay coil 5i actuates an armature 53 engaging a normally closed contact 5e. The armature is connected to the line 56, and by a line 55 to a contact 5e of a four-pole quick acting relay 5l having armatures S0 and 33 engaging contacts 5e and 62 respectively. The relay 57 is provided with a coil 5d which is connected by a line 59 to the contact 5cl of the relay 52. The coil 5i! is also connected to the source of positive plate potential for the tube d2. The armature Sil of the relay 5l' is connected to ground at iii. The armatures 53 and t2 connect an inductive reactance @fi through leads @5 and @6 to an alternating current power line di.' which is preferably the line from which the receiver 3i) is energized.

In the operation of the system of Fig. 2, the audio frequency output of the receiver 30, after passing through the transformer 33, is rectified by the rectifier tube and causes a unidirectional current t/.i flow through the resistor 35 in the direction of the arrow, producing a potential drop across that resistor in a direction to supply a negative bias with respect to ground to the lead Lit. The value of this bias due to audio frequency signals of predetermined values overcomes the positive bias produced by the battery 3l and biases the control grid li of the tube A2 negative to the point oi cut-oit so that no current ilows in the plate circuit of the tube 42. When a silence occurs, however, or the audio frequency output of the receiver 3@ falls below a predetermined value the negative voltage drop across the resistor 35 is removed, allowing the battery il to introduce a positive bias to the control grid 4l which causes the tube e2 to become conductive. rIhe tube l2 passes a heavy plate current which flows through the coil 5I of the slow actingr relay 52. Plate current also flows through the closed contact of the relay 52 through the line e@ to the coil 58 of the quick acting relay 5l'. The relay 5l thereupon irnmediately actuates its armature to close contacts 56 and t2. Closing of the contact B2 throws the reactory E4!- across the line i'd and serves to increase the reactive volt-arnperes on the line 6l by one unit. Closing of the contact 56 connects the coils 5i and E@ of the relays 52 and El to ground and establishes a holding circuit for these relay from the source of plate potential to ground.

After a predetermined period of time, the slow acting relay armature 53 is actuated to break the Contact till. IThis breaks the circuit to the coil 58 of the relay 5l immediately releases that relay. Releasing the relay 5l disconnects the reactor 512 from the line @l and breaks the holding circuit of the relays 52 and 5l. If the tube l2 has ceased conducting by the time the holding circuit is broken, the relay bf2 is restored to a normal and the system is in a condition to respond to the next silent period. If, however, the tube l2 is still conducting, the relay 52 remains open until the end of the period of silence which causes the tube @2 to be conducting. Consequently, the reactance 6.1i is connected across the line Eil for a predetermined period of time which is independent of the length of the period of silence which initiated the operation of the relay.

A period of silence which is sufficiently eX-` tended to operate the fast relay 51 will thus oonnect the reactor 6d to the line 5'! for the predetermined fixed period of time. At the end of this silence period, or at the end of the nxed period, wichever is longer, the slow relay will return to its normal position and the home unit will be in condition to respond to the next period of silence. This fixed period of time may, of course, constitute only a fraction of a second and is only suicient to allow the recorder to be actuated at the monitoring station. The period is preferably maintained as short as possible in order to reduce the possibility or interference with the record due to changes in the reactive load from other causes during the measuring and recording period.

If the system is to respond to acoustic levels other than zero, the bias of the battery iii may be adjusted accordingly. The system may, for example, be adjusted to respond to acoustic levels higher than normal or in a given range. rlhe system may be made responsive to signals of a selected frequency only by including a suitable iilter ahead of the tube 3E. Combinations of these systems may also be used.

Referring to Figs. 3. and 4, one of the monitoring systems is shown as a standard radio receiver i5 connected to an antenna l5 and assumed to be tuned to the same broadcast program as the radio receiver 3@ of Fig. 2. In the case of a net- Work program, the program may be received from different stations by the home receiver and the monitor. The receiver '15 may be of any standard type providing an audio frequency output which is supplied by lines l: to the primary i8 of a transformer '13. The transformer 'is is provided with a pair of secondaries SB and Si which are connected to control circuits A and B respectively for producing respectively the control and the inhibiting signals.

The secondary 3d is series connected through a resistor 32 with a rectifier tube 83 and a resistor 84, by-passed by condenser 85. The resistor S4 is grounded at 8 through a battery 3l which is connected to supply a positive bias with respect to ground. A limiting tube 8S, to which a negative bias is supplied by a biasing battery ES, is connected across the tube 23 and resistor 34. The connections are such that the audio frequency output from the receiver 'i5 causes a f rectified current to ilow in the direction or" the arrow through the resistor Srl for producing a voltage drop across that resistance. The negative end of the resistor Sli is connected through a line 9o and resistor 9| to the control grid 92 of an amplifier tube 93. The connections are such that with a normal audio frequency output to the secondary 8l?, the voltage drop across the resistor 8d produces a negative bias with respect to ground which is sufficient to block the tube 93. However, during silence periods, the battery 8'! supplies a positive bias through the line 9? to the control grid S2 which causes the tube 93 to function. rlhe tube 93 accordingly functions only during the silence period;

rlhe control grid 92 is also supplied with an alternating voltage from an oscillator 95 which is connected through a lead 98 and condenser 9i to the grid 92. The oscillator 95 may be of any standard type adapted to operate continuously to produce a continuous signal and to supply the same to the control grid S2. however, is amplied by the tube S3 only during the silence periods when a positive bias is supplied to the control grid from the battery''l. v`The tube t8 and biasing battery 39 constitute a limiter to prevent the negative bias supplied to the line te trom becoming excessive. Ii' the battery sii is or the same potential as the battery 8l, then the potential drop across the resistor Sli' will only become sufficient to equal the potential o the battery 8l and cancel the positive bias produced thereby. In that event the bias on the grid 92 would vary from the positive value of the battery El to zero. It is to be understood, however, that suitable adjustments may be made to produce the desired operating eiect and that the selected acoustic level may be other than zero as in the ease oi the home receiver circuit.

The tube 93 is shown as provided with a cathode l which is connected through resistor i1 and condenser and biasing battery 103 to ground at Iil, and with a screen grid H35 which is connected through a resistor 165, by-passed by condenser icl, to a source of positive biasing potential. A second control grid i i@ is connected to-input lines iii to receive an inhibiting signal from the other monitors to be described. A suppressor grid i i2 is connected to the cathode i. An anode ill is connected by an output lead H5 and a resistor i i@ to a source of positive plate potential. The arrangement is such that during audio frequency silence periods an A. C. voltage from the oscillator c5 appears in the lead 1 15, but during normal periods of operation with an audio frequency output, the tube 93 is blocked and no signal appears on the lead H5.

-The audio control circuit B connected to the secondary 8i is similar to the control circuit A except that the circuit B produces a negative signal during silence periods. For this purpose, the secondary Si is connected through a resistor 123 to a rectifier tube il and a resistor 222 in series circuit. A condenser i23 is connected across the resistor i22. During periods of audio frequency output to the secondary 8l, a rectified current passes through the resistor i122 in the direction of the arrow, producing a voltage drop thereacross. The negative end of the resistor E22 is connected through a biasing battery 124 to ground at 125. The battery l24 is connected to supply a negative bias with respect to ground to the resistor i22. A limiter tube l2ia` with a biasing battery iii is connected across the tube 12i and resistor 122 to limit the voltage drop produced across the resistor |22.

' The positive end o the resistor 22 is connected by a lead i3d and a condenser 132 to a grounded resistor 133.

Y During normal audio frequency output periods the positive voltage drop across the resistor i22 balances the negative bias of the battery 124 so that the lead iti remains substantially at ground potential. However, during silent periods when no current novvs through the resistor 22, the lead receives the negative bias from the battery 121i. A negative pulse is thus supp 'ed to the condenser 13g and resistor 33 during silent periods. Any positive pulses on the line i3d are bypassed to ground through a rectifier tube 134 which is connected in parallel to the resistor 133.

- The resistor 33 and the rectier tube 134 are connected by a lead Hit to the control grid 1371 of a tube 13S and through a condenser 139 to the anode 14D of a tube ll.

The tubes and lili are provided with cathodes 142 and M3 which are connected to ground at M4, and with anodes and 14B which are connected respectively through resistors M6 and 14T to a source oi positive plate potential.

The cathodes are connected through a biasing battery Hit and resistor |49 to the control grid |5il of the tube lill. The grid |50 is connected through resistor |52 to an output lead |53 and to the anode |45.

In the operation of this gate circuit the tube |33 is normally conducting since its grid bias is zero while that of tube is negative. This latter tube may be biased near cut-01T by means of battery Hi8. Vhen a negative pulse is applied to lead |36 it causes tube i355 to temporarily stop conducting. When this happens the potential of plate its suddenly becomes more positive and plate |155 assumes the positive potential of the plate supply. This positive increment of voltage is applied resistor BW and part of this pulse is applied to grid lil. rThis causes tube |4| to conduct temporarily. As a result, the plate of this tube, Mt, suddenly drops in positive potential and current drawn through condenser |39 while this condenser is charging to its new potential. This current is drawn through resistor |33, thus causing a negative voltage to be established on grid lill. Luring the time that condenser |39 is charging, this negative potential is maintained on grid |3l and tube |33 is maintained non-conducting. After the condenser |39 has fully charged to its new value of potential, current ceases t ow through resistor and when this happens the bias on tube |38 is removed. IThis causes tube |33 to become conducting again. The plate M then drops suddenly in potential and this negative pulse is applied to resistor' |52. Part of this drop is applied to grid l5@ and tube |4| is rendered nonnconducting again. This circuit now remain at rest until another negative pulse is applied to lead It is noted that the time during which the tube |38 remains non-conducting is dependent on the time that condenser |39 takes to fully acquire its charge and stop current from flowing through resistor |33. Thus, the length of the output pulse which apepars on lead |53 may be adjusted by means of the time constant of resistor |33 and condenser |3g. A timed negative pulse is thus produced in the output lead |53 which is independent oi the length of the input pulse or oi the silent period which produced such pulse.

The lead |53 is connected through a condenser it to a grounded resistor 25| and thence to inhibiting leads The leads |62 are connected to the amplifier tube grids of the other monitors correspondi z to the second control grid H0 of tube s3 and grid 255 of tube as later discussed. Likewise the lead il i supplying the second control grid i it or the tube is connected to receive the inhibiting potential from the various monitors tuned to other radio programs.

Hence when a silence occurs on any of the radio programs to which the other monitors are tuned, an inhibiting signal is supplied to the lead l l which prevents the tube from functioning and the lead llt connected to the anode ||4 of the tube 93 carries a sinusoidal current only during periods of silence on the program to which the receiver 'l5 is tuned and provided no silence occurs in the programs to which the other monitors are tuned so as to introduce a simultaneous signal on lead lli.

The lead H5 is connected through a condenser il@ to a rectifier tube ill which is grounded at |'i2 and across which a resistor |l3 and by-pass condenser illl are connected to ground. The rectifier tube lli is connected to rectify the output of the tube 93 and to cause a direct current nega- 8 tive pulse to be produced across the resistor |13. This voltage is smoothed out by the condenser IM so that a negative signal appears during the periods of audio silence on the radio. The resistor |73 and rectifier lll are connected through a condenser and lead litt to a rectifier tube |821, ley-passed by a grounded resistor |32, which constitute a differentiator network adapted to convert the sharp voltage rise across the resistor |13 into a relatively large negative pulse. The diode |8| short circuits any positive pulses which may appear in the lead H33 so as to prevent such positive pulses from affecting the subsequent circuits. The lead |83 accordingly carries negative pulses corresponding to the periods of audio frequency silence in the receiver l5.

The lead |83 is connected to the control grid |84 (Fig. 4) of a tube |85 and through a condenser IBS to the anode |8l' of a tube |88. The anodes |89 and itl are connected through ren sistors |96 and li respectively to a source of positive plate potential. The 'tubes |65 and |32 are provided with cathcdes ist and lull respectively which are grounded at |98 and are connected through a biasing battery its, lead 2S@ and resistor 20| to the control grid N2 of tube |83. Grid 262 is also connected through a resistor 203 to a lead 2M and to the anode |89.

The tubes |35 and |88 are connected to opn crate as a gate circuit similar to the tubes |33 and l, and are adapted to produce an output pulse in the lead 2M, the duration oi which is independent ol' the duration of the input pulse on the lead |83. The tube |35 is normally conducting and the tube |88 is normally non-conducting. Upon the application of a negative pulse to the grid ISS the tube it becomes non-conducting and the tube hlt becomes conducting. When the tube becomes non-conducting the potential of the anode |l9 rises due to the removal of the voltage drop through the resistor ist. Hence a positive pulse is applied to lead 2M. When the tube |88 becomes conducting the bias voltages of the tubes are aiected so as to cause the tube |85 f to again become conducting and the tube |83 to become non-conducting. The period required for this cycle depends upon the values of the condenser |36 and of the resistor |82 and is independent of the duration of the negative signal supplied by the input lead |83. Hence a timed positive DC pulse is produced in the output lead 204.

The positive pulse on the lead 2M is connected through a condenser 2 l l) and lead 2 l to the control grid 2|2 of an amplifier tube 2lb having a cathode 2 I ll which is connected to ground through a biasing battery 2|5. The tube 2|3 has an anode 2|6 connected by a lead 2 to a brake coll 220 and thence to a source of positive plate potential. A resistor 22| is connected from the lead 2|| to ground.

The brake coil 22E! is connected to energize a magnet 225 which applied a magnetic drag to a disc 226 connected to a shaft EN of a standard var meter 228 Which is adapted to position the shaft 221 in accordance with the reactive volt amperes of the power line 6l. The tube 2|3 is normally biased to cut-01T, but is caused to become conducting due to the positive pulse on the lead 2|| and, While conducting, actuates the brake circuit of the var meter 228. Hence during such periods a drag is applied to the var meter 228 Which prevents the same from responding to any change in inductive load oi the power line B1 during such periods.

A second var meter 230 is connected to the power line 61 and is provided with a shaft 23| which is positioned in accordance with the inductive load on the line 551. The shafts 221 and 23! are connect-ed respectively to rotate a pair of coils 232 and which are so positioned that when the var meters 228 and 232 are indicating the same reactive lcad the axes of the coils 232 and 233 are displaced by 9G degrees so that there is no magnetic coupling between such coils. When the relative positions or the axes vary from 90 degrees, however, a magnetic coupling is produced which is dependent upon the relative angles.

One of the coils, shown as the coil 233, is connected to a source of alternating current 234, for example a 1000 cycle oscillator. The other coil 232 is connected by a lead 235 to a variable tap 233 on a resistor 23'J which is connected in series with a condenser 238 between the lead 224 and ground. The other end of the coil 232 is connecte ed by a lead 242 to a control grid 24| of a tube 242 having a cathode 243 which is connected through a resistor 244, by-passed by condenser 245, and through a biasing battery 243 to ground. The tube 242 is provided with an anode 241 which is connected by a lead 243 and a resistor 243 to a source of plate potential.

For small angles not exceeding l to 2O degrees the voltage generated in the coil 232 as a result of the magnetic coupling with coil will be proportional to the angle between the shafts 221 and 23|. Hence the voltage in the lead 242 consists of a portion of the D. C. voltage drop across the resistor 23'! and an alternating voltage derived from the coil 233 whose magnitude is proportional to the angle between the axes or the coils 232 and 233.

The tube 242 is normally biased to cut-off by means of battery 245, but is made conducting "'13 due to the positive pulse supplied from the resistor 231. Hence for the duration of the timed positive pulse in the lead 224 the tube 242 operates as an amplifier to amplify the A. C. voltage received from the coil 232. Inasmuch as the var meter 228 has been rendered sluggish due to the magnetic brake during the period of the positive pulse on the line 224, the var meter 223 is prevented from registering the increment in reactive-volt-amperes in the power line during the measurement period, whereas the var meter 235 responds to such increment. The angular difference between the shafts accordingly constitutes a measure of the increment of reactivevolt-amperes in the power line 51 during the measurement period.

The output lead 248 of the tube 242 is connected through a condenser 255 to the control grid 256 of an amplifier tube and to a resistor 234. Resistor 234 is connected to lead 265 which is connected to input lines Hi to receive the inhibitor signals from the other monitors. Should a silence occur on any of the other monitors, tube 251 will be rendered non-conducting and its output will be Zero. Consequently, the recorder will cease to record.

Tube 251 has a cathode 258 which is connected to ground through a resistor 259 and a by-pass condenser 262, and has an anode 23| which is connected by an output lead 252 and a resistor 263 to a source of positive plate potential. The lead 282 is connected through a condenser 2l@ to a rectifier tube 21| across the output of which a resistor 212 is connected. The operation is such that a direct current is passed through the re- 10 sistor 212 proportional to the alternating voltage supplied by the lead 248 to the amplifier tube 242. Hence the voltage drop produced across such resistor is proportional to the increment in reactive-volt-amperes being measured.

The voltage drop across the resistor 2l'2 is supplied by a lead 213 to a suitable recording device 214 which may constitute a voltmeter or a continuous recorder. A recorder is preferably used in order to obtain a continuous and permanent record.

To summarize the operation of the monitor system oi Figs. 3 and 4, the receiver 15 is tuned to the program which is to be monitored and is adapted to produce the usual audio frequency output signal. This output signal is applied through the transformer 19 and secondaries 80 and 8| to the two control signal circuits A and B. The control circuit B produces a negative inhibiting pulse during periods of audio silence and the control circuit A produces a positive control pulse during such silent periods. The positive control pulse from the circuit A is supplied to the control grid of the amplifier tube 33 which is normally so biased that this positive control signal renders the tube conductive. At the same time the negative inhibiting signal from the circuit B is supplied by the lead |62 to the am plier tubes of the other monitors corresponding to tubes 93 and 251 and prevents them from operating. Hence the monitors are prevented from producing a control signal or from recording even though their gate circuits may have started to function.

An alternating voltage is supplied by the oscillator 95 to the tube 93 and is amplified by that tube when the tube becomes unblocked by the positive control signal from the circuit A. The alternating current output of the tube 93 is supplied by the lead ||5 to the rectifier 1| which is connected to produce a negative D. C. pulse across the resistor |13 during periods when the tube 93 is conducting. This pulse passes through the filter circuit comprising the condensers |14 and |82 and resistor |82 and any positive pulse is short circuited by the rectier tube I8 l. Hence a negative pulse appears on the lead |83 whenever the tube 93 is made conductive by a positive pulse from the control circuit A.

The negative pulse on the lead |83 is applied to the grid |84 of the gate circuit tube |85 which is normally conducting. This negative pulse causes the tube |85 to become non-conducting and the gate circuit, including the tubes |85 and |88, is so adjusted that the tube |85 remains nonconducting for a predetermined period of time, regardless of the duration of the negative pulse which initiated the action. This results in a timed positive pulse in the output lead 204 which is applied to the control grid 2 |2 of the tube 2|3. The tube 2|3 is thus made conducting for the predetermined period of time and energizes the brake coil 220 to apply a -drag to the var meter 228. During this same period of time the tube 242 is made conductive through the positive bias supplied from the resistor 231 and transmits an alternating voltage which is dependent upon the relative angular positions of the coils 232 and 233. This voltage, after amplication in the tubes 242 and 251 and rectification in the tube 21|, produces a unidirectional voltage across the resistor 212, the value of which is recorded on the recorder 214.

The adjustments of these circuits are preferably so made that the recordings take place a fraction of a second after the reactors 64 have been connected to the line 6l, so as to eliminate the eTect of any pulses which might take place at the instant of connection.

It will be evident that the recorded signal .is independent of the total reactive-volt-amperes in the power line 5l and is responsive only to the increment in reactive-volt-amperes after the brake coil 22@ has been energized.

It is to be understood that in practice, if for example four major network stations are to be monitored, a separate monitor will be provided for each of these stations and other monitors would be tuned to the stations not aliated with the networks. The other monitors would be connected to produce the inhibiting signal and would inhibit all the network recorders whenever one of these non-network stations had a period of silence. The actual recording may taire place in only a fraction of a second so that the influence of other reactive loads on the power line would have a minimum of opportunity of affecting the record. The recorder 2M may of course be graduated to read directly in number oi sets. As each set introduces a unit reactance onto the line, the total number of units connected at any one time may be readily determined.

Assuming, for example, that a hundred diiferent home units are in. the group to be sampled and that each one of these home units is provided with the circuit shown at the left of Fig. 1, including a reactance I9, which has a value of one unit. Then, if ten of these receivers are tuned to program A, for example, the ten reactors I9 will be thrown on and oir of the line simultaneously when there is a silence in the received program. This will result in increasing the total reactance on the line l2 by ten units. It should be noted that these reactance pulses may be of short duration, such as a fraction of a second and may occur several times a second, as between the syllables of a spoken word. Hence they will occur at irregular intervals and in a timed sequence corresponding to the instantaneous changes in a signal level of the program.

Referring now to Fig. l and assuming that only these ten home receivers are in operation, the var meters 223 and 23@ will both register 0 before the reactances I9 are thrown on the line. During the instant when the ten reactances I9 are thrown on the line, however, the var meter 228 will continue to register 0 due to the drag exerted by the disc 226. The var meter 230, however, will register ten units of inductance. This ten unit differential in the readings of the two var meters is registered on the recorder 214 as above described and indicates that ten receivers are tuned to Station A.

Now assuming that twenty other receivers are tuned to a station, such as station B, the inductances I 9 associated with these other receivers will be thrown on and off the line in a timed sequence, depending upon the program being broadcast by Station B. Except in rare instances, however, the inductances i9 of the receivers tuned to Station B would not be thrown on the line at the same instant as the ten inductances of the receivers which have been assumed to be tuned to the Station A.

Assuming now that a silent period on Station B occurs slightly before a silence period occurs on Station A, then the twenty inductors of the twenty receivers tuned to Station B would be thrown on the line and would produce an inductance of twenty units on the line, which would be registered by var meters 228 and 23D. If now the silence period on Station A should occur while these other inductances are still on the line, the ten additional inductances i9 would be thrown on the line raising the total inductance on the line to thirty units which would be registered by the var meter 23). However, the var meter 228 would remain at twenty units due to the drag of the disc 2E@ and the difference in reading of ten units would represent the number of stations tuned to Station A. Hence the indication on the recorder 214 which is made at the time of the silences on Station A will give an accurate measurement of the number of home units tuned to that station regardless of whether other units are tuned at the same time to different stations and regardless of whether other inductors may be connected to the line during the time when the inductcrs of the receivers tuned to Station .A are inserted.

It will be noted that the above described system does not require the cooperation of the broadcasting station, but only requires that the main power line be available for eecting the measurement. The system is practically instantaneous in operation and produces a continuous record of the listener reaction.

The monitor system of Figs. -3 and 4 has been described as responsive to silence periods. It may, however, be varied as described above to respond to other program characteristics as in the case of the home unit of Fig. 2, and in any event would respond to the same characteristic as the home receivers.

Although a specic circuit for accomplishing this result has been set forth for purposes of illustration, it is to be understood that changes and modifications may be made therein as will be apparent to a person skilled in the art. Only so much of the circuit has been shown as is necessary to an understanding of the invention. The circuit will, of course, include various contrcls, sources of potential, etc. which are well known in the art. Also the individual elements of the circuit may be varied. The invention is only to be restricted in accordance with the scope of the following claims.

What is claimed is:

l. The method of determining whether a remote radio receiver which is tunable to any one of a plurality of dierent radio broadcast programs is tuned to a selected one of said programs, which comprises deriving from the remote receiver a time sequence based on the recurrence of selected normally irregularly recurring changes in instantaneous signal intensity of the signals or the program being received thereby, monitoring said selected program by a monitor receiver independently of said remote receiver, simultaneously deriving a time sequence based on the recurrences of the saine selected normally irregularly recurring changes in instantaneous signal intensity of the signals being received by said monitor receiver, and comparing the time sequences or said selected changes which are derived at the same instants from said remote received and from said monitor receiver to determine their coincidence or lack of coincidence.

2. A radio listener survey system comprising a plurality of radio broadcast receivers tunable to a plurality of broadcast transmitters, a known electrical load at each receiver, means at each receiver responsive to the acoustic level of the received program and adapted to produce a control signal when the acoustic level reaches a predetermined value, an electrical conducting line at each receiver connected to a central point, a timed relay to connect said load to said line, and means responsive to said control signal to actuate said relay, a monitoring receiver tuned to a selected broadcast transmitter and having means producing a control signal in response to said predetermined acoustic level, means measuring the increment in load on said line, and means responsive to the control signal of said monitoring receiver to actuate said measuring device.

3. A radio listener survey system comprising a plurality of monitoring receivers tuned to different selected broadcast transmitters and havaudio frequency output circuits carrying audio signals, a control circuit connected to each output circuit and responsive only to a predeterminati characteristic of said signal, said contr circuits each having means producing a conroi signal and an in lbiting signal, an electrical conducting ne, a device for measuring the load on said line, a circuit responsive to said control signal ci each monitor to render` said measurderioe operative, and a circuit responsive to the inhibiting signal of each monitor to pren vent operation of the measuring devices of all other monitors.

A radio listener survey system comprising a monitoring receiver tuned to a selected broadnected 'o said output circuit and responsive only vl-etermined normal characteristic of said i voge across said resistor which is a function of the received signal, a circuit conected to respond to said unidirectional volt- 'f and to produce a timed voltage pulse of a given dura-tion regardless of the duration of said voltage, a load carrying line, a measuring device to measure the increment in load on said and means responsive to said 'timed pulse to actuate said measuring device.

5. n, radio listener survey system comprising a monitoring receiver tuned to a selected broadcast transmitter and having an output circuit carrying a received signal, a control circuit connected to said output circuit and responsive only to a predetermined characteristic of said signal, said control circuit comprising a rectier and a resistor connected to develop a unidirectional voltage across said resistor which is a function of said received signal, a source of alternating voltage` an ampliner connected to amplify said alternating voltage, connections supplying the potential drop across said resistor as a control bias for said amplifier tube and arranged to render said amplier tube conductive only during periods when said received signal has a predetermined value, means rectifying the alternating potential output of said amplifier tube to produce negative pulse corresponding in duration to the periods of operation of said ampliiier tube, a timed gate circuit including a pair of tubes connected to respond to said negative pulse and to produce a positive pulse of a given duration regardless of the duration of said negative pulse, a load carrying line, a pair of measuring devices connected to measure the load on said line and having shafts carrying coils normally positioned in non-inductive relationship when said measuring devices have the same reading and shiftable by said shafts to inductive relationship in response to a diiference in readings of said measuring devices, a magnetic brake associated with one of said measuring devices, means including an amplifier tube actuated by said timed positive pulse to render said brake effective during the period of said pulse to prevent changein reading of said braked device whereby the difference in readings of said device represents the increment in load during said period, an alternating voltage source connected to excite one of said coils, an amplier tube connected to respond to the voltage induced in the other of said coils, means responsive to said timed positive pulse to render said last amplifier tube operative during the period of said timed pulse, and a responsive device connected to the output ci 'cuit of said last amplier tube.

6. A radio listener survey system comprising a plurality of monitoring receivers tuned to selected broadcast transmitters and having output circuits carrying received signals, a pair of control circuits connected to said output circuit of each monitoring receiver and responsive only to a predetermined characteristic of said signal, said control circuits each comprising a rectier and a resistor connected to develop a unidirectional voltage across said resistor which is a function of said signal, a source of alternating voltage, an ampliier connected to amplify said alternating voltage, connections supplying the potential drop across said resistor of one of said control circuits as a control bias for said amplier tube and arranged to render said amplifier tube conductive only during periods when said signal has a, predetermined value, connections supplying the potential drop across said resistor of the other control circuit as a control bias for the corresponding amplifier tubes of the other monitoring receivers to block said other amplier tubes during said period, means rectifying the alternating potential output of said amplifier tube to produce a negative pulse corresponding in duration to the periods of operation of said amplier tube, a timed gate circuit including a pair of tubes connected to respond to said negative pulse and to produce a timed positive pulse of a given duration regardless of the duration of said negative pulse, a load carrying line, a pair of measuring devices connected to measure the load on said line and having shafts carrying coils normally positioned in noninductive relationship when said measuring devices have the same reading and shiftable by said shafts to inductive relationship in response to a difference in readings of said devices, a magnetic brake associated with one of said devices, means including an amplifier tube actuated by said timed positive pulse to render said brake effective during the period of said pulse to prevent change in reading of said braked device Whereby the difference in readings represents the increment in load during said period, an alternating voltage source connected to excite one of said coils, an amplier tube connected to respond to the voltage induced in the other of said coils, means responsive to said timed positive pulse to render said last amplier tube operative during the periods of said timed pulse, and a responsive device connected to the output circuit of said last amplier tube.

'7. A radio listener survey system comprising a plurality of radio broadcast receivers tunable to a plurality of broadcast transmitters, a known electrical load at each receiver, a control circuit connected to each receiver and having means responsive to a given normal, recurring characteristic of the received program, an electrical conducting line at each receiver connected to a central point, a relay circuit actuated by said control circuit to connect said electrical load across said line, a monitoring receiver tuned to a selected broadcast transmitter and having a control circuit having means responsive to the given program characteristic, a measuring device connected to measure the total electrical load on said line, and means actuated by said last control circuit to actuate said measuring device.

8. A radio listener survey system comprising a plurality of radio broadcast receivers tunable to a plurality of broadcast transmitters, a known electrical load at each receiver, a control circuit connected to the output of each receiver and having means responsive to a given acoustic level or the received program, an electrical conducting line at each receiver connected to a central point, a relay circuit actuated by said control circuit to connect said electrical load across said line, a monitoring receiver tuned to a selected broadcast transmitter and having a control circuit having means responsive to the given acoustic level, a measuring device connected to measure the total electrical load on said line, and means actuated by said last conn trol circuit to actuate said measuring device.

9. A radio listener survey system comprising a plurality of radio broadcast receivers tunable to a plurality oi broadcast transmitters, a known electrical load at each receiver, a control circuit connected to the output of each receiver and having means responsive to periods of audio silence of the received program, an electrical conducting line at each receiver connected, to a central point, a relay circuit actuated by said control circuit to connect said electrical load across said line, a monitoring receiver tuned t a selected broadcast transmitter and having a control circuit having means responsive to said periods of audio silence, a measuring device to measure the total electrical load on said line, and means actuated by said last control circuit to actuate measuring device.

1G. A radio l lner survey system comprising a plurality of iodio bread receivers and tunable to a plura ty of broadcast transmitters, a

known reactive load at each receiver, a control of audio silence to produce a control impulse, a measuring device to measure the total reactive load on said line, and means actuated by said last control impulse to actuate said measuring device.

11. A radio listener survey system comprising a plurality oi radio broadcast receivers tunable to a plurality of broadcast transmitters, a known electrical load at each receiver, a control circuit connected to the output of each receiver and having means responsive to a normal, recurring program characteristic of the received program to produce a control impulse, an electrical conducting line at each receiver connected to a central point, a timed relay circuit actuated by said control impulse to connect said load across said line for a predetermined period of time regardless of the duration of the control impulse, a monitoring receiver tuned to the selected broadcast transmitter and having a control circuit having means responsive to said normal, recurring program characteristic to produce a control impulse, a device to measure the total load on said line, and means actuated by said last control impulse to actuate said measuring device during the period of connection of said electrical loads at said receivers.

3.2. A radio listener survey system comprising p" ality oi radio broadcast receivers tunable to a plurality of broadcast transmitters, a known electrical load at each receiver, a control circuit connected to the output of each receiver and having means responsive to a normal, recurring program characteristic of the received program to produce a control impulse7 an electrical conducting line at each receiver connected to a central point, a relay circuit actuated by said con trol impulse to connect said electrical load across said line, a plurality of monitoring receivers tuned to selected broadcast transmitters, each monitor having a control circuit having means responsive to said normal, recurring program characteristic to produce a control signal and an inhibiting signal, each monitor having a measuring device to measure the total load on said line, means actuated by the control signal of each monitor to actuate its measuring device, and means actuated by the inhibiting signal of each monitor to prevent actuation of the measuring devices of all other monitors.

WILLIAM D. HORN. JOHN R. RAGAZZINI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,096,109 Hopkins Oct. 19, 1937 2,188,165 Thomas Jan. 23, 1940 2,249,324 Potter July 15, 1941 2,393,060 Reagan Jan. 15, 1946 2,397,475 Dinga Apr. 2, 1946 

